The present invention relates to a method of reducing iron ores into pig iron in a shaft furnace, especially a blast furnace, wherein coke and oil (e.g. fuel oil) are used as the reducing agents and the oil is added through at least one pipe having a nozzle head to the blast furnace blast air heated to a high temperature and being blown into the blast furnace via a blast tuyere, whereby said pipe and said nozzle head, at least in portions thereof, are subjected to the high temperature of the blast air supplied to the blast furnace.
When injecting oil or fuel oil through the blast tuyeres of a blast furnace, substantial difficulties due to variations of the blast air pressure and of the blast temperature may result from the fact that these parameters substantially affect the blast air velocities within the blast tuyere and also the viscosity of the blast air or flue gas.
It has been found that variations of the blast velocity have a noticeable effect on the optimum distribution and combustion of the injected volume of the oil. Such variations of the blast velocity occur primarily in the case of failure and, for instance, in connection with the change-over of the hot blast stoves of regenerators.
In order to avoid uncomplete oil combustion within the blast tuyere and, therefore, to avoid damage of the latter, it has already been considered to automatically stop the oil supply at the respective oil injection nozzle when a minimum value of the hot blast through-put is reached; however, great difficulties have been reported in these respects (compare Klepzig: "Fachberichte", July 1969, page 477).
Actually, in the conventional method there does not so much exist the difficulty of burning out of the blast tuyere; rather, due to the ON-OFF control associated therewith, the disadvantage of very substantial variations of the volume of oil supplied exists, which disadvantage in the coal-oil balance of a blast furnace becomes apparent in a deciding manner with respect to the freedom from trouble in the furnace operation or furnace working especially when the proportion of the oil is high, i.e. between 100 and 200 kg of oil per (metric) ton of pig iron, with a coke proportion which is thus reduced to from 500 to 400 kg per ton of pig iron. If the known minimum switch-over value of the oil supply is too high, the oil supply is stopped too frequently; if, on the other hand, this value is too low, there are frequent intervals with too high a quantity of oil, i.e., with uneconomical operation and black smoke formation in the furnace.
Primarily, however, simple switching on and off raises problems with respect to the cooling of the oil lance.